1. Field of the Invention
The present invention relates, in general, to wireless signal transmission systems and apparatus and, specifically, to wireless transmission system capable of transmitting audio or video signals in either analog or digital format via high frequency carrier signals in the 900 MHz or higher range.
2. Description of the Art
Various wireless audio and video signal transmission systems have been devised which transmit audio and/or video signals, such as television signals, radio signals, etc., by a wireless link from a signal source to a signal receiver or output device capable of converting the received signals to audio and/or video sounds.
Local wireless television transmission systems which transmit television or radio signals from a local source, such as a television, VCR, radio set or radio stereo receiver, frequently transmit such signals within a frequency band above 900 MHz and, preferably, within a frequency band of 902 MHz to 928 MHz. This frequency band is desirable because at higher carrier frequencies, the bandwidth of the transmitted signal occupies a smaller region of the transmission bandwidth than at lower carrier frequencies. This leaves more channels available for use and results in decreased RF interference and noise as well as greater flexibility in channel selection.
Many televisions and radio stations now include stereo audio signals in their transmissions. Thus, a wireless signal transmission apparatus must have a capability of transmitting stereo audio signals. Conventionally, stereo audio signals are transmitted by adding the right and left audio channels to form a first signal and subtracting the right and left channels to form a second signal which is modulated on a subcarrier of 38 KHz. The subcarrier is suppressed and the combination of the first signal, the subcarrier modulated second signal, and a 19 KHz pilot signal form a multiplexed stereo signal which modulates a carrier for transmission to a remote receiver. Conventional integrated circuits for producing such multiplexed stereo signals, known as stereo encoder circuits, are available commercially.
Such high frequency wireless transmission systems conventionally include a transmitter which is capable of transmitting television or radio mono or stereo signals to a remote receiver, both having appropriate antennas for transmitting and receiving the source signals as a modulated high frequency carrier. Heretofore, the remote receiver has been mounted in close proximity to or formed as a part of a signal output device, such as an AM/FM stereo receiver, television, for example. The distance or separation between the remote receiver antenna and the output device is relatively limited due to the low power level signals transmitted at the high carrier frequency. This small transmission range limits the use of additional speakers or an additional receiver and speakers which may not be located in the same general area as the first transmitter and the output device.
Audio and video signals are now available through the Internet typically in the form of streaming broadcast of radio or television programs, recorded music, etc. The audio and/or video signals are downloaded from the Internet signal source by a user's Internet service provider and input through a modem to the user's computer. The computer generates signals to an audio and/or video output card which then transmits analog output signals to speakers coupled to the computer or to a monitor for broadcast of the signals.
Frequently, however, the audio system or the monitor employed with a computer is not as sophisticated as the user's home stereo system or television. Further, a user's computer may not be located in the same room or area of a home as the multi-component stereo system or television.
Thus, it would be desirable to provide a wireless signal transmission apparatus which is capable of retransmitting high frequency audio and/or video signals modulated on a high frequency carrier by a first transmitter and transmitted wirelessly via the high frequency carrier to a remote receiver over an expanded transmission range as compared to previously devised high frequency transmission systems. It would also be desirable to provide a wireless high frequency signal transmission system which is capable of transmitting streaming broadcast signals from the Internet or any other audio and/or video source to a remote receiver.